Acrylic pressure sensitive adhesive and pressure sensitive adhesive tape

ABSTRACT

The purpose of the present invention is to provide an acrylic pressure sensitive adhesive and a pressure sensitive adhesive tape preferable to be used for adhesion and fixation of members to be used in closed space of such as a vehicle, a housing where odors become a problem; or in the side of electronic appliances where volatile gases become a problem and also relates to a vehicular air conditioner unit produced by using them. 
     The present invention relates to an acrylic pressure sensitive adhesive, which has 500 ppm or lower of volatile component concentration A calculated by the following equation (1), when the acrylic pressure sensitive adhesive is heated at 90° C. for 30 minutes:
 
volatile component concentration A (ppm)=volatile component content X (μg)/pressure sensitive adhesive weight Z (g) before heating   (1)
 
     in the equation (1), the volatile component content X is an amount measured by conversion into toluene.

TECHNICAL FIELD

The invention relates to an acrylic pressure sensitive adhesive and apressure sensitive adhesive tape preferable to be used for adhesion andfixation of members to be used in closed space of such as a vehicle, ahousing where odors become a problem; or in the inside of electronicappliances where volatile gases become a problem and also relates to avehicular air conditioner unit produced by using them.

BACKGROUND ART

Double coated tapes to be used for adhesion and fixation of members havebeen used in a vehicle and a housing as well as in the inside ofelectronic appliances. However, recently, problems of the use of thesepressure sensitive adhesive tapes have been pointed out. For example,there occurs fogging attributed to high boiling point volatilecomponents in glass in an automotive inside or operation failureattributed to high boiling point volatile components and impurities alsoin members of the inside of electronic appliances in some cases.Accordingly, a pressure sensitive adhesive tape to be used in closedspace of vehicles such as automobiles and housings, electronic applianceinsides is strongly required to be scarcely odorous and have a low totalamount of volatile gases, which are environmental burden substances.

Meanwhile, in Japan, guidelines of decrease of respective interiorvolatile organic compounds but also decrease of the total of thevolatile organic compounds for countermeasures for so-called sick housesin the housing field are issued from Ministry of Health, Labour, andWelfare. Also, German Association of the Automotive Industry (Verbandder Automobilindustrie (VDA)) has determined an evaluation method forodors of members to be used for the automotive insides in VDA 270 andalso evaluation methods for volatile components in DVA 277 and VDA 278.Further, in order to determine the behavior of the fog attributed tovolatile components emitted from members, Deutsches Institut fur Normunghas determined in DIN No. 75201. As described, it is required todecrease not only specific volatile substances but also a variety ofvolatile substances in various fields.

The causes of the volatile gases emitted from a common pressuresensitive adhesive tape may include a remaining solvent, a remainingmonomer, a remaining polymerization initiator, a tackifier to be usedfor improving the pressure sensitive physical properties, and the like.Also, the causes of odors may include volatile gas and the like.

Japanese Kokai Publication Hei-6-122859 discloses a method for obtaininga pressure sensitive adhesive scarcely containing a remaining monomer bypolymerizing a monomer having a high molecular weight and a lowsaturated steam pressure. Further, Japanese Kokai PublicationHei-2-115291 discloses a pressure sensitive adhesive using an acrylicpolymer obtained by polymerization of a specific acrylic monomer tolower the odor. On the other hand, Japanese Kokai Publication 2002-69411discloses a production method for a pressure sensitive adhesive tapecomprising a pressure sensitive adhesive obtained by using a high purityacrylic polymer with few volatile components such as a remaininginitiator or an unreacted monomer produced at a high polymerizationratio by solution polymerization at a specified reaction temperatureusing a specified amount of an azo type polymerization initiator.Japanese Kokai Publication 2002-309210 discloses a pressure sensitiveadhesive tape at a low gas emission level obtained by blockcopolymerization. Further, Japanese Kokai Publication Hei-11-315260discloses a production method for a hot melt type pressure sensitiveadhesive tape as an anti-fogging pressure sensitive adhesive tape.

However, even in the case of these pressure sensitive adhesive tapes,there still remains a problem that in the case the tapes are used inclosed space in housings, vehicles, the insides of electronicappliances, the odor suppression is insufficient by simply suppressingspecific volatile components, so that the odor cannot be decreased to aninsensible level. Also, high boiling point volatile components in thecase of adding a tackifier are not taken into consideration andtherefore, with respect to a common pressure sensitive adhesivecontaining the tackifier, no satisfactory effect has been achieved byconventional techniques.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an acrylic pressuresensitive adhesive and a pressure sensitive adhesive tape preferable tobe used for adhesion and fixation of members to be used in closed spaceof such as a vehicle, a housing where odors become a problem; or in theside of electronic appliances where volatile gases become a problem andalso relates to a vehicular air conditioner unit produced by using them.

A first aspect of the present invention provides an acrylic pressuresensitive adhesive, which has 500 ppm or lower of volatile componentconcentration A calculated by the following equation (1), when theacrylic pressure sensitive adhesive is heated at 90° C. for 30 minutes:volatile component concentration A (ppm)=volatile component content X(μg)/pressure sensitive adhesive weight Z (g) before heating   (1)in the equation (1), the volatile component content X is an amountmeasured by conversion into toluene.

A second aspect of the present invention provides an acrylic pressuresensitive adhesive, which has 600 ppm or lower of volatile componentconcentration B calculated by to the following equation (2), when theacrylic pressure sensitive adhesive is heated at 120° C. for 30 minutes:volatile component concentration B (ppm)=volatile component content Y(μg)/pressure sensitive adhesive weight Z (g) before heating   (2)in the equation (2), the volatile component content Y is an amountmeasured by conversion into n-hexadecane.

The acrylic pressure sensitive adhesive of the first aspect of thepresent invention or second aspect of the present invention preferablycontains a tackifier containing 13% by weight or lower of the componentwith 600 or lower of molecular weight.

The third aspect of the present invention provides a pressure sensitiveadhesive tape, which has a pressure sensitive adhesive layer comprisingthe acrylic pressure sensitive adhesive of the first aspect of thepresent invention or the second aspect of the present invention, thepressure sensitive adhesive tape having 300 ppm or lower of volatilecomponent concentration C calculated by the following equation (3), whenthe pressure sensitive adhesive tape is heated at 90° C. for 30 minutes:volatile component concentration C (ppm)=volatile component content P(μg)/pressure sensitive adhesive tape weight R (g) before heating   (3)in the equation (3), the volatile component content P is an amountmeasured by conversion into toluene.

The fourth aspect of the present invention provides a pressure sensitiveadhesive tape, which has a pressure sensitive adhesive layer comprisingthe acrylic pressure sensitive adhesive of the first aspect of thepresent invention or the second aspect of the present invention, thepressure sensitive adhesive tape having 400 ppm or lower of volatilecomponent concentration D calculated by the following equation (4), whenthe pressure sensitive adhesive tape is heated at 120° C. for 30minutes:volatile component concentration D (ppm)=volatile component content Q(μg)/pressure sensitive adhesive tape weight R (g) before heating   (4)in the equation (4), the volatile component content Q is an amountmeasured by conversion into n-hexadecane.

Accordingly, a vehicular air conditioner unit which is obtainable byusing the pressure sensitive adhesive tapes of the third aspect of thepresent invention or the fourth aspect of the present invention is alsoone of the present invention.

DETAILED DISCLOSURE OF THE INVENTION

The invention is described in detail below.

The first aspect of the present invention provides an acrylic pressuresensitive adhesive, which has 500 ppm or lower of volatile componentconcentration A calculated by the following equation (1), when theacrylic pressure sensitive adhesive is heated at 90° C. for 30 minutes:volatile component concentration A (ppm)=volatile component content X(μg)/pressure sensitive adhesive weight Z (g) before heating   (1)in the equation (1), the volatile component content X is an amountmeasured by conversion into toluene.

If the volatile component concentration A is 500 ppm or lower under theabove-mentioned condition, no odor problem occurs even if the tape isused in closed space of such as a vehicle and housing.

The above-mentioned volatile component content X can be measured byheating a weighed acrylic pressure sensitive adhesive at 90° C. for 30minutes using a thermal desorption apparatus (e.g. ATD-400, manufacturedby PerkinElmer Inc.) and measuring the volatile component contentemitted at that time by GC-MS apparatus (e.g. Automass II-15,manufactured by JEOL Ltd.). That is, an accurately weighed acrylicpressure sensitive adhesive of about 20 mg is put in a sample tube(inner diameter about 5 mm, length about 10 cm) and heated at 90° C.while helium gas being circulated at 1.5 mL/min for 30 minutes and theemitted volatile components are collected in a trap tube installed in athermal desorption apparatus and concentrated and then the trap tube isheated at 280° C. for 10 minutes and introduced into the GC-MS. ForGC-MS measurement, a non-polar capillary column (HP-1, manufactured byAgilent Technologies, 0.32 mm×60 m×0.25 μm) is used and the temperatureof the column is kept at 40° C. for 4 minutes and then heated to 100° C.at 5° C./min heating rate and further to 320° C. at 10° C./min heatingrate and kept at 320° C. for 3 minutes. The MS measurement range is 30to 400 amu, the He flow rate is 1.5 mL/min, the ionization voltage is 70eV, the ion source is kept at 230° C., the interface at 250° C., and thetransfer line 225° C. The volatile component content can be calculatedfrom the obtained peak surface area by conversion into toluene weightbased on an absolute calibration curve produced by using toluene.

With respect to the acrylic pressure sensitive adhesive of the firstaspect of the present invention, the total amount of the remainingpolymerization initiator detected by the above-mentioned measurementconditions is preferably 30 ppm or lower and the total amount of theacrylic monomer is preferably 50 ppm or lower, and the volatilecomponent content is preferably 50 ppm or lower after 30 minutes orlonger retention time. In such cases, odor is further decreased.

The second aspect of the present invention provides an acrylic pressuresensitive adhesive, which has 600 ppm or lower of volatile componentconcentration B calculated by to the following equation (2), when theacrylic pressure sensitive adhesive is heated at 120° C. for 30 minutes:volatile component concentration B (ppm)=volatile component content Y(μg)/pressure sensitive adhesive weight Z (g) before heating   (2)in the equation (2), the volatile component content Y is an amountmeasured by conversion into n-hexadecane.

If the volatile component concentration B is 600 ppm or lower under theabove-mentioned condition, not only no odor problem occurs but also thetotal amount of high boiling point volatile components is a little, sothat no fogging problem taken place and even if the tape is used in theinside of an electronic appliance, the tape does not cause a problem.

The above-mentioned volatile component content Y can be measured in thesame method as that in the case of the acrylic pressure sensitiveadhesive of the first aspect of the present invention. The amount iscalculated by keeping the column temperature at 50° C. for 2 minutes,heating to 160° C. at 25° C./min heating rate and then to 300° C. at 10°C./min heating rate and keeping at the temperature for 20 minutes inGC-MS measurement and carrying out calculation from the obtained peaksurface area by weight conversion based on an absolute calibration curveproduced by using n-hexadecane.

The acrylic pressure sensitive adhesive of the present inventioncontains an acrylic polymer as a main component. The above-mentionedacrylic polymer is not particularly limited and preferably, for example,a homopolymer of a (meth)acrylic acid ester monomer or a copolymer ofthe (meth)acrylic acid ester monomer with another vinyl monomercopolymerizable with the monomer.

Examples of the (meth)acrylic acid ester monomer are preferably estersof acrylic acid or methacrylic acid with a primary or a secondaryalcohol comprising an alkyl group having 4 to 12 carbon atoms.

Another vinyl monomer copolymerizable with the above-mentioned(meth)acrylic acid ester monomer is used for heightening agglomerationforce by modification of the acrylic polymer and for example, thosewhich have high glass transition point (Tg) themselves and increase Tgof the polymer to be obtained and those which contribute to meshstructure formation of polymer molecules by crosslinking reaction of thefunctional group contained in the molecules of them with an externallyadded crosslinking agent can be used.

Examples of the above-mentioned vinyl monomers which can increase Tg ofthe polymer to be obtained are styrene, acrylonitrile, methylmethacrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate,N-phenylmaleimide, N-cyclohexylmaleimide, and N-vinylpyrrolidone. Also,examples of the vinyl monomers which contribute to mesh structureformation of polymer molecules by crosslinking reaction of thefunctional group contained in the molecules with an externally addedcrosslinking agent are carboxyl-containing monomers such as acrylicacid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, andmaleic anhydride; hydroxyl-containing monomers such as 2-hydroxyethyl(meth)acrylate, n-methylolacrylamide; and epoxy-containing monomers suchas glycidyl acrylate, and allyl glycidyl ether.

In the case the above-mentioned acrylic polymer is the copolymer of the(meth)acrylic acid ester monomer and another vinyl monomercopolymerizable with the ester monomer, the content of the (meth)acrylicacid ester monomer is preferably 70% by weight or higher in the monomercomposition. Also, in the case the vinyl monomer is for increasing Tg ofthe polymer to be obtained, the content of such a vinyl monomer ispreferably 30% by weight or lower. In the case the vinyl monomer is forcontributing to mesh structure formation of polymer molecules bycrosslinking reaction of the functional group contained in the moleculeswith an externally added crosslinking agent, the content of such a vinylmonomer may be controlled so as to keep the functional group-containingmonomer preferably in a range of 0.1 to 10% by weight, more preferablyin a range of 0.05 to 5% by weight.

The above-mentioned acrylic polymer can be obtained by polymerization ofthe above (meth)acrylic acid ester monomer or copolymerization of amixture of the above (meth)acrylic acid ester monomer and the vinylmonomer copolymerizable with it. The polymerization method is notparticularly limited and conventionally known polymerization methods,for example, a solution polymerization (boiling point polymerization,below boiling point polymerization), emulsion polymerization, suspensionpolymerization, mass polymerization, living polymerization can beexemplified. Among them, the solution polymerization using neither asurfactant nor a dispersant is preferable.

A polymerization initiator to be used in the case of polymerization ofthe above-mentioned acrylic polymer is not particularly limited and forexample, a peroxide type polymerization initiator and an azo typepolymerization initiator are preferable.

As the above-mentioned polymerization initiator, those having a 10-hourhalf-life of 80° C. or lower so as to leave no volatile component of thepolymerization initiator or its residue in the acrylic polymer to beobtained. A single polymerization initiator may be used or two or moretypes of polymerization initiators may be used in combination.

The above-mentioned peroxide type polymerization initiator is notparticularly limited and examples of it are organic peroxides such asperoxycarbonate, ketone peroxide, peroxyketal, hydroperoxide, dialkylperoxide, diacyl peroxide (lauroyl peroxide, benzoyl peroxide,3,5,5-trimethylhexanoyl peroxide), and peroxy ester. Among them, peroxyesters with 8 or more carbon atoms of the acid residue and 6 or fewercarbon atoms of the alcohol residue are preferable in terms of odorsuppression of the acrylic polymer to be obtained. Examples of theperoxy esters are tert-hexylperoxy-2-ethylhexanoate,tert-butylperoxy-2-ethylhexanoate,tert-butylperoxy-3,5,5-trimethylhexanoate, and tert-butylperoxylaurate.

Diacyl peroxide of which the acyl group is aliphatic with 8 or morecarbon atoms is also preferable. Examples of such diacyl peroxide arelauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide,and stearoyl peroxide.

The above-mentioned azo type polymerization initiator is notparticularly limited and examples of it are azocompounds such as2,2′-azobis(isobutyronitrile), 2,2′-azobis(2-methylbutyronitrile),2,2′-azobis(2,4-dimethylvaleronitrile), and2,2′-azobis(dimethylisobutyrate).

In the case of polymerization of the above-mentioned acrylic polymer, asthe above-mentioned polymerization initiator, it is preferable to selectthose having a 10-hour half-life of 80° C. or lower so as to leave novolatile component of the polymerization initiator or its residue in thereaction solution and to carry out the reaction as long as possible,while keeping at the temperature higher than 10-hour half-lifetemperature as the polymerization condition. Further, in order todecrease the remaining polymerization initiator after polymerization andto promote the reaction quickly and completely, it is preferable to keepthe polymerization temperature T in the final stage of thepolymerization in a range satisfying the conditions defined by thefollowing equation (5) and to keep the polymerization temperature for along duration.t _(1/2)+25≧T≧t _(1/2)+5  (5)t_(1/2) is 10-hour half-life temperature.

As the above-mentioned acrylic polymer, it is more preferable as theunreacted monomer, the unreacted polymerization initiator, or otherimpurities are less and at the time of polymerization or on completionof the polymerization, it is preferable to carry out operation forremoving the unreacted monomer, the unreacted polymerization initiator,and other impurities.

The practical means for decreasing the remaining monomer in theabove-mentioned polymerization step are, for example, a method forseparating and removing the remaining monomer in a refluxing solvent inthe terminal stage of the polymerization and a method for adding ascavenger monomer with a low boiling point and easy to be removed byreaction with the acrylic monomer or a modified vinyl monomer in theterminal stage of the polymerization.

The above-mentioned method for removing the remaining monomer from thepolymerization system may include a method for replacing the refluxingsolution of the polymerization solvent with a new solvent; a method foradding a scavenger monomer with a relatively low boiling point such asvinyl acetate, vinyl butyl ether, methyl acrylate, or styrene at themoment the polymerization degree reaches 95% or higher, preferably 98%or higher and then removing the remaining monomer with the scavengermonomer; and a method for washing the acrylic polymer with a poorsolvent against the acrylic polymer, which is a low boiling pointsolvent such as methanol, ethanol, n-hexane, or n-heptane, on completionof the polymerization. These methods may be employed solely or two ormore of the methods in combination.

The acrylic pressure sensitive adhesive of the invention may contain atackifier for the purpose of improving the pressure sensitive adhesionphysical properties. In the case of using the above-mentioned tackifier,the content of the component with a molecular weight of 600 or lower ispreferably 13% by weight or lower. If such a tackifier is employed, thevolatile component emitted from the tackifier can be suppressed withoutdeteriorating the pressure sensitive adhesion physical properties, thepressure sensitive adhesion physical properties are improved, and theacrylic pressure sensitive adhesive with suppressed odor can beobtained. Further, the volatile component to be released in the case ofheating acrylic pressure sensitive adhesive to be obtained at 120° C.for 30 minutes can be suppressed to 600 ppm or lower based onn-hexadecane and the amount of the volatile component which is a highboiling point component difficult to be removed by drying and has 30minutes or longer retention time can be suppressed to 50 ppm or lower.The molecular weight and the content of the tackifier can be measured byGPC and calculated from the surface area ratio and the value obtained byconversion in to polystyrene.

Examples of the tackifier are rosin resins, rosin-modified phenolresins, disproportionation rosin ester resins, polymerized rosin esters,hydrogenated rosin ester resins, terpene phenol resins, cumarone indeneresins, alkylphenol resin, and petroleum resins. Among them, alicyclicsaturated hydrocarbon resins belonging to the rosin resins, polymerizedrosin resins, and petroleum resins are preferable since they can removethe low molecular weight component.

The method for removing the component with a molecular weight of 600 orlower from the above-mentioned tackifier may include a method forheating and melting the tackifier at a softening point or higher and amethod for blowing steam. In the case of the method for heating andmelting the tackifier, in order to prevent oxidation reaction withoxygen in air, it is preferable to carry out heating in an inert gassuch as nitrogen, helium or the like. Also, the heating time ispreferably about 1 to 5 hours in order to avoid decomposition of thetackifier by the heating. In the case of blowing steam, if steam isblown after heating and melting of the tackifier followed by decrease ofthe tackifier to about 1 to 50 kPa, the volatile component can bedecreased and the odor can be suppressed. The duration for blowing steamis preferably about 1 to 5 hours. If it is shorter than 1 hour, theeffects to decrease the volatile gas and suppress the odor areinsufficient and even if it is longer than 5 hours, the treatmenteffects are not so much improved.

The content of the above-mentioned tackifier is not particularlylimited, and it is preferably 0.1 to 35% by weight to the acrylicpolymer.

The acrylic pressure sensitive adhesive of the invention may contain acrosslinking agent. Addition of the crosslinking agent is effective toincrease the agglomeration force since crosslinking structure of thepolymer molecules or the polymer and the tackifier is formed by reactionof it with the functional group of the acrylic polymer or the tackifier.The above-mentioned crosslinking agent is not particularly limited andmay include, for example, isocyanate type crosslinking agents, aziridinetype crosslinking agents, epoxy type crosslinking agent, and metalchelating type crosslinking agent.

The acrylic pressure sensitive adhesive of the invention may furthercontain, on the basis of the necessity, additives such as a plasticizer,an emulsifier, a softening agent, a filler, a pigment and, a dye. It ispreferable for them to be subjected similarly to proper removal of thevolatile components as much as possible.

The acrylic pressure sensitive adhesive of the invention is suitable fora pressure sensitive adhesive layer of a pressure sensitive adhesivetape. The pressure sensitive adhesive tape having the pressure sensitiveadhesive layer containing the acrylic pressure sensitive adhesive of theinvention can be used preferably for adhesion and fixation of members tobe used in a closed space of such as a vehicle, a housing and, in theinside of an electronic appliance, where odorous gases become a problem.

The third aspect of the present invention provides a pressure sensitiveadhesive tape which has a pressure sensitive adhesive layer comprisingthe acrylic pressure sensitive adhesive of the first aspect of thepresent invention or the second aspect of the present invention, thepressure sensitive adhesive tape having 300 ppm or lower of volatilecomponent concentration C calculated by the following equation (3), whenthe tape is heated at 90° C. for 30 minutes.volatile component concentration C (ppm)=volatile component content P(μg)/pressure sensitive adhesive weight R (g) before heating   (3)In the equation (3), the volatile component content P is an amountmeasured by conversion into toluene.

The fourth aspect of the present invention provides a pressure sensitiveadhesive tape which has a pressure sensitive adhesive layer containingthe acrylic pressure sensitive adhesive of the first aspect of thepresent invention or the second aspect of the present invention, thepressure sensitive adhesive tape having 400 ppm or lower of volatilecomponent concentration D calculated by the following equation (4), whenthe tape is heated at 120° C. for 30 minutes.volatile component concentration D (ppm)=volatile component content Q(μg)/pressure sensitive adhesive weight R (g) before heating   (4)In the equation (4), the volatile component content Q is an amountmeasured by conversion into n-hexadecane.

The above-mentioned volatile component content P or volatile componentcontent Q can be measured by the same method as the cases of the acrylicpressure sensitive adhesives of the first aspect of the presentinvention and the second aspect of the present invention.

The pressure sensitive adhesive tapes of the invention may comprise onlythe pressure sensitive adhesive layers containing the acrylic pressuresensitive adhesives of the invention or the above-mentioned pressuresensitive adhesive layers layered on one face or both faces of asubstrate.

The substrate is not particularly limited and may include, for example,paper, non-woven fabrics, and sheet-like formed bodies made ofpolyesters, polyolefins, polyurethanes, polychloroprenes, vinyl chlorideresin, and acrylic resins. Also, the above-mentioned substrate may besubjected to foaming treatment. The substrate is preferable for to bemade of a previously refined material and to be subjected to the removalof the volatile components to satisfy the suppression of odor.

The production method of the pressure sensitive adhesive tape of theinvention is not particularly limited and a conventionally known methodcan be employed. For example, a method for forming the pressuresensitive adhesive layer directly on the substrate; a method for formingthe pressure sensitive adhesive layer on paper subjected to releasetreatment and then transferring the pressure sensitive adhesive on theprocess paper to the substrate can be exemplified.

As the method for forming the pressure sensitive adhesive layer, amethod for applying the acrylic pressure sensitive adhesive of theinvention in a prescribed thickness on the substrate or process paperand drying the solvent can be exemplified. At the time of drying thesolvent, a method for increasing a drying temperature as high aspossible to the extent that no foaming occurs in the substrate or theprocess paper, a method for prolonging the retention time in the dryingfurnace, a method for setting the drying furnace to be negativepressure, and a method for increasing the drying air blow amount can beemployed, and accordingly, the volatile component concentrationremaining in the pressure sensitive adhesive tapes of the invention canfurther be decreased. These methods may properly be selected andemployed in combination. Also, in the case of curing and maintaining thepressure sensitive adhesive tapes of the invention, the volatilecomponents can be suppressed by adjusting the curing temperature,decreasing the pressure in the curing atmosphere and accordingly thevolatile component concentration can be decreased and the odor can besuppressed.

If the pressure sensitive adhesive tapes of the invention are used, anadhesive structure in which volatile gas emission attributed to thepressure sensitive adhesive tapes and affecting electronic appliances isscarcely caused and odor emission attributed to the pressure sensitiveadhesive tapes is suppressed can be formed. The pressure sensitiveadhesive tapes are particularly suitable for the use relevant to theautomotive interiors where the spaces are narrow and odor becomes aproblem and particularly a vehicular air conditioner unit produced byusing the pressure sensitive adhesive tapes of the invention isremarkably improved in odor suppression as compared with those producedby using conventional pressure sensitive adhesive tapes.

Accordingly, a vehicular air conditioner unit which is obtainable byusing the pressure sensitive adhesive tapes of the third aspect of thepresent invention or the fourth aspect of the present invention is alsoone of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the invention will be described more in detail withreference to Examples, however the invention should not be limited tothese Examples.

EXAMPLE 1

In a reaction container equipped with a thermometer, a starrier, acooling pipe, a dropping funnel, and a nitrogen gas introduction pipe, amonomer mixture containing n-butyl acrylate 70 g, 2-ethylhexyl acrylate27 g, acrylic acid 3 g, and 2-hydroxyethyl methacrylate 0.5 g wasdissolved in ethyl acetate 83 g and at a refluxing point, as apolymerization initiator, lauroyl peroxide (10-hour half-life: 62° C.) 4mmol was added properly from the starting of the polymerization for 4hours to polymerize the acrylic monomers. After 4 hours, thepolymerization initiator 2 mmol was properly added for 4 to 6 hours todecrease remaining monomers and after that, for further decreasing theremaining monomers and remaining initiator, the reaction was carried outfurther for 10 hours (the polymerization terminal stage). The obtainedsolution was cooled to produce an acrylic polymer solution.

The obtained acrylic polymer solution 100 g was mixed evenly with afunctional isocyanate type crosslinking agent [Coronate L (activesubstance 55%), manufactured by Nippon Polyurethane Industry Co., Ltd.]1.5 g to produce an acrylic pressure sensitive adhesive.

The obtained acrylic pressure sensitive adhesive was applied in athickness of 60 μm after drying to one face of a separator of a 50μm-thick polyethylene terephthalate film and dried for complete removalof the solvent at 120° C. for 5 minutes to produce a pressure sensitiveadhesive tape.

EXAMPLE 2

An acrylic pressure sensitive adhesive and a pressure sensitive adhesivetape were produced in the same manner as Example 1, except thattert-hexylperoxy-2-ethylhexanoate (10-hour half-life: 70° C.) was usedas the polymerization initiator.

EXAMPLE 3

An acrylic pressure sensitive adhesive and a pressure sensitive adhesivetape were produced in the same manner as Example 1, except thattert-butylperoxy-2-ethylhexanoate was used as the polymerizationinitiator.

EXAMPLE 4

An acrylic pressure sensitive adhesive and a pressure sensitive adhesivetape were produced in the same manner as Example 3, except that vinylacetate monomer 5 g was added after 10 hours from reaction.

COMPARATIVE EXAMPLE 1

An acrylic pressure sensitive adhesive and a pressure sensitive adhesivetape were produced in the same manner as Example 1, except thatbenzoylperoxide (10-hour half-life: 74° C.) was used as thepolymerization initiator.

EXAMPLE 5

A tackifier 25 g containing 9.4% by weight of a component with amolecular weight of 600 or lower was added to 100 g of the acrylicpolymer produced in the same manner as Example 4 and evenly stirred andthen an isocyanate type crosslinking agent [Coronate L (active substance55%), manufactured by Nippon Polyurethane Industry Co., Ltd.] 1.5 partsby weight was added and the resulting mixture was again stirred evenlyto produce an acrylic pressure sensitive adhesive.

The obtained acrylic pressure sensitive adhesive was applied in athickness of 60 μm after drying to one face of a separator of a 50μm-thick polyethylene terephthalate film and dried at 120° C. for 5minutes to produce a pressure sensitive adhesive tape.

COMPARATIVE EXAMPLE 2

An acrylic pressure sensitive adhesive and a pressure sensitive adhesivetape were produced in the same manner as Example 5, except that atackifier 25 g containing 15.6% by weight of a component with amolecular weight of 600 or lower was added.

EXAMPLE 6

An acrylic pressure sensitive adhesive and a pressure sensitive adhesivetape were produced in the same manner as Example 4, except thattert-butylperoxy-2-ethylhexanoate (10-hour half-life: 70° C.) 4 mmol wasproperly added as the polymerization initiator in a period of 4 hoursfrom the starting and after 4 hours, 3,5,5-trimethylhexanoyl peroxide 2mmol was further properly added for decreasing the remaining monomers.

EXAMPLE 7

An acrylic pressure sensitive adhesive and a pressure sensitive adhesivetape were produced in the same manner as Example 5, except that theacrylic polymer produced in Example 6 was used.

The acrylic pressure sensitive adhesives and pressure sensitive adhesivetapes produced in Examples 1 to 7 and Comparative Examples 1 and 2 wereevaluated for odorous properties, cloud, volatile componentconcentrations, and physical properties by the following methods. Theresults are shown in Table 1.

(Evaluation of Odorous Properties)

Evaluation was carried out according to VDA 270. The evaluation wascarried out by enclosing each pressure sensitive adhesive tape with 50cm² size in a glass bottle of 1 L capacity, taking out the tape afterkeeping the tape at 40° C. atmosphere for 24 hours, and immediatelysubjecting the tape to the odorous properties evaluation based on thefollowing 6-point method. At the sensory evaluation, three or morepanelists evaluated each pressure sensitive adhesive tape according tothe following 6-point method and the average values were calculated:

-   1: impossible to be sensed;-   2: possible to be sensed but not offensive;-   3: possible to be clearly sensed but not so much offensive;-   4: offensive;-   5: very offensive; and-   6: not endurable    (Evaluation of Cloud)

Evaluation was carried out by enclosing each pressure sensitive adhesivetape about 20 g in a glass bottle of 100 mL capacity, covering thebottle with a glass plate, heating at 120° C. for 24 hours, andobserving the change of the glass plate. The determination criteria forthe evaluation were as follows:

-   ◯: no change observed;-   Δ: a trace of fog observed; and-   ×: fog observed clearly.    (Measurement of the Volatile Component Concentrations)

The volatile component content was measured by heating a weighedpressure sensitive adhesive tape by a thermal sorption apparatus(ATD-400, manufactured by PerkinElmer Inc.) at the time when the tapewas heated at 90° C. for 30 minutes and also at time when the tape washeated at 120° C. for 30 minutes and measuring the emitted volatilecomponent contents by GC-MS apparatus (e.g. Automass II-15, manufacturedby JEOL Ltd.) and, the volatile component concentration was calculatedaccording to the above-mentioned equation (3) or (4). The volatilecomponent concentration of each pressure sensitive adhesive wascalculated according to the above-mentioned equation (1) or (2) from thepressure sensitive adhesive weight (the pressure sensitive adhesiveweight=the pressure sensitive adhesive tape weight—the substrate PETweight) calculated by previously measuring the weight ratio of thesubstrate PET in the pressure sensitive adhesive tape and subtractingthe substrate weight from the pressure sensitive adhesive tape weight.With respect to the PET substrate, it was previously confirmed thatthere was no volatile component for the measurement.

For GC-MS measurement, a non-polar capillary column (HP-1, manufacturedby Agilent Technologies, 0.32 mm×60 m×0.25 μm) was used and in the caseof heating at 90° C. for 30 minutes, the temperature of the column waskept at 40° C. for 4 minutes and then heated to 100° C. at 5° C./minheating rate and further to 320° C. at 10° C/min heating rate and keptat 320° C. for 3 minutes. Also in the case of heating at 120° C. for 30minutes, the temperature of the column was kept at 50° C. for 2 minutesand then heated to 160° C. at 25° C./min heating rate and further to300° C. at 10° C./min heating rate and kept at the temperature for 20minutes.

The MS measurement range was 30 to 400 amu, the He flow rate was 1.5mL/min, the ionization voltage was 70 eV, the ion source was kept at230° C., the interface at 250° C., and the transfer line at 225° C. Thevolatile component concentration was calculated from the obtained peaksurface area by weight conversion based on an absolute calibration curveproduced by using toluene or n-hexadecane.

The remaining polymerization initiator total amount and the remainingacrylic monomer total amount after heating at 90° C. for 30 minutes andthe volatile component content after 30 minutes or longer retention timewere also measured.

(Evaluation of Physical Properties)

The adhesion of each of the obtained pressure sensitive adhesive tapeswas measured according to JIS Z0237.

TABLE 1 after 30 minutes after 30 minutes at 90° C. (ppm) at 120° C.(ppm) pressure pressure pressure sensitive pressure sensitive adhesivetape sensitive sensitive adhesive component adhesive adhesive tapeadhesion volatile volatile content after remaining total volatilevolatile against peeling component component 30 minutes polymerizationremaining component component from SUS at concen- concen- or longerinitiator monomer concen- concen- 180° C. tration A tration C retentiontime amount amount tration B tration D odor cloud (N/25 mm) Example 1135 90 16 26 15 120 80 3.2 ◯ 9.5 Example 2 116 77 18 20 20 111 74 2.6 ◯9.7 Example 3 113 75 17 17 21 110 73 2.6 ◯ 9.3 Example 4 98 65 15 15 10105 70 2.5 ◯ 9.7 Example 5 330 220 33 14 11 357 238 2.7 ◯ 17.2 Example 678 52 13 13 10 95 63 1.5 ◯ 9.6 Exemple 7 315 210 37 10 8 353 235 2.3 ◯18.1 Comparative 533 355 38 63 160 674 449 5.5 Δ 9.9 Example 1Comparative 960 640 478 14 10 1575 1050 5.0 Δ 16.5 Example 2

INDUSTRIAL APPLICABILITY

The invention provides an acrylic pressure sensitive adhesive and apressure sensitive adhesive tape preferable to be used for adhesion andfixation of members to be used in closed space of such as a vehicle, ahousing where odor become a problem; or in the inside of electronicappliances where volatile gases become a problem and also provides avehicular air conditioner unit produced by using them.

1. An acrylic pressure sensitive adhesive containing an acrylic polymerand a tackifier, wherein the acrylic polymer is polymerized with apolymerization initiator having a 10-hour half-life at 80° C. or lowerand under a polymerizing condition carrying out the reaction whilekeeping at the temperature higher than 10-hour half-life temperature andkeeping the polymerization temperature T in the final stage of thepolymerization in a range satisfying the condition defined by thefollowing equation 5, wherein the tackifier contains 13% by weight orlower of a component with 600 or lower molecular weight, which has 500ppm or lower of volatile component concentration A calculated by thefollowing equation (1), when the acrylic pressure sensitive adhesive isheated at 90° C. for 30 minutes:volatile component concentration A (ppm)=volatile component content X(μg)/pressure sensitive adhesive weight Z (g) before heating   (1) inthe equation (1), the volatile component content X is an amount measuredby conversion into toluenet½+25≧T≧t½+5   (5) wherein t½ is 10-hour half-life temperature.
 2. Anacrylic pressure sensitive adhesive containing an acrylic polymer and atackifier, wherein the acrylic polymer is polymerized with apolymerization initiator having a 10-hour half-life at 80° C. or lowerand under polymerizing condition carrying out the reaction while keepingat the temperature higher than 10-hour half-life temperature and keepingthe polymerization temperature T in the final stage of thepolymerization in a range satisfying the conditions defined by thefollowing equation (5), wherein the tackifier contains 13% by weight orlower of a component with 600 or lower molecular weight, which has 600ppm or lower of volatile component concentration B calculated by to thefollowing equation (2), when the acrylic pressure sensitive adhesive isheated at 120° C. for 30 minutes:volatile component concentration B (ppm)=volatile component content Y(μg)/pressure sensitive adhesive weight Z (g) before heating   (2) inthe equation (2), the volatile component content Y is an amount measuredby conversion into n-hexadecanet½+25≧T≧t½+5  (5) wherein t½ is 10-hour half-life temperature.
 3. Apressure sensitive adhesive tape, which has a pressure sensitiveadhesive layer comprising the acrylic pressure sensitive adhesiveaccording to claim 1, the pressure sensitive adhesive tape having 300ppm or lower of volatile component concentration C calculated by thefollowing equation (3), when the pressure sensitive adhesive tape isheated at 90° C. for 30 minutes:volatile component concentration C (ppm)=volatile component content P(μg)/pressure sensitive adhesive tape weight R (g) before heating   (3)in the equation (3), the volatile component content P is an amountmeasured by conversion into toluene.
 4. A pressure sensitive adhesivetape, which has a pressure sensitive adhesive layer comprising theacrylic pressure sensitive adhesive according to claim 2, the pressuresensitive adhesive tape having 400 ppm or lower of volatile componentconcentration D calculated by the following equation (4), when thepressure sensitive adhesive tape is heated at 120° C. for 30 minutes:volatile component concentration D (ppm)=volatile component content Q(μg)/pressure sensitive adhesive tape weight R (g) before heating   (4)in the equation (4), the volatile component content Q is an amountmeasured by conversion into n-hexadecane.
 5. A vehicular air conditionerunit, which is fixed by the pressure sensitive adhesive tape accordingto claim
 3. 6. A pressure sensitive adhesive tape, which has a pressuresensitive adhesive layer comprising the acrylic pressure sensitiveadhesive according to claim 1, the pressure sensitive adhesive tapehaving 300 ppm or lower of volatile component concentration C calculatedby the following equation (3), when the pressure sensitive adhesive tapeis heated at 90° C. for 30 minutes:volatile component concentration C (ppm)=volatile component content P(μg)/pressure sensitive adhesive tape weight R (g) before heating   (3)in the equation (3), the volatile component content P is an amountmeasured by conversion into toluene.
 7. A pressure sensitive adhesivetape, which has a pressure sensitive adhesive layer comprising theacrylic pressure sensitive adhesive according to claim 2, the pressuresensitive adhesive tape having 400 ppm or lower of volatile componentconcentration D calculated by the following equation (4), when thepressure sensitive adhesive tape is heated at 120° C. for 30 minutes:volatile component concentration D (ppm)=volatile component content Q(μg)/pressure sensitive adhesive tape weight R (g) before heating   (4)in the equation (4), the volatile component content Q is an amountmeasured by conversion into n-hexadecane.
 8. A vehicular air conditionerunit, which has adhered thereto the pressure sensitive adhesive tapeaccording to claim
 4. 9. A vehicular air conditioner unit, which hasadhered thereto the pressure sensitive adhesive tape according to claim6.
 10. A vehicular air conditioner unit, which has adhered thereto thepressure sensitive adhesive tape according to claim 7.